Myeloperoxidase deficiency

Myeloperoxidase (MPO) deficiency is one of the most common inherited disorders of phagocytic cells, characterized by the absence or marked reduction of the enzyme myeloperoxidase in neutrophils and monocytes. MPO is a key enzyme in the oxygen-dependent antimicrobial system of neutrophils, playing an important role in the killing of bacteria and fungi by generating hypochlorous acid and other reactive oxidants within phagolysosomes. The condition is caused by mutations in the MPO gene located on chromosome 17q23.1. Despite the important role of MPO in innate immunity, the vast majority of individuals with MPO deficiency are clinically asymptomatic and are often identified incidentally through automated differential blood counts that use peroxidase-based staining. The immune system compensates through other antimicrobial mechanisms, including the oxygen-independent killing pathways. However, in a small subset of patients — particularly those with concurrent conditions such as diabetes mellitus — MPO deficiency can be associated with an increased susceptibility to infections, most notably disseminated candidiasis and other fungal infections. Bacterial infections may also occur but are less commonly reported as a significant clinical problem. There is no specific treatment for MPO deficiency itself. Management is primarily supportive and focused on the prompt recognition and aggressive treatment of infections when they occur. Patients with coexisting diabetes mellitus or other immunocompromising conditions should be monitored more closely for infectious complications. Antifungal therapy is used when candidal or other fungal infections develop. Genetic counseling may be offered to affected families. The prognosis for the overwhelming majority of individuals with MPO deficiency is excellent, with most living entirely normal lives without significant infectious complications.

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